Bone cutting and breaking apparatus, and miniaturized cutting head

ABSTRACT

The present invention includes an apparatus and method for cutting a bone including a cutting assembly having a cutting blade, a cutting guide for guiding the shape of the cut in the bone, and a power source for powering the cutting blade. The cutting blade is moveable radially to vary the depth of the cut in the bone, and the cutting blade is capable of cutting around the circumference of the bone as well as in a longitudinal direction along the bone. A powered bone breaking device for completing the breaking of the weakened bone is also disclosed. A miniaturized version of the bone cutting apparatus can be used to cut out sections of a femur head from inside a femur body.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to apparatus used in the cuttingand breaking of bones in certain medical procedures.

[0003] 2. Description of the Related Art

[0004] Certain medical procedures require the surgeon to break a bone.Examples of these procedures are bone lengthening operations thatrequire the insertion of a bone lengthening device or other prosthesis.The conventional manner of performing this operation usually requiresremoving the bone marrow in the center of the bone by drilling throughone end of the bone down its longitudinal axis to create a cavity in thebone marrow in which the bone lengthening nail or prosthesis is to befit.

[0005] After this cavity has been drilled, holes are generally drilledperpendicular to the bone at the site where the bone is to be broken.Once the holes are drilled, a chisel is inserted into this region anddriven through the bone section and twisted to cause the bone section tobreak.

[0006] The bone lengthening nail is then inserted into the cavity sothat the upper portion is lodged in one-half of the broken bone and thelower portion of the nail is lodged in the lower portion of the brokenbone. The nail is periodically lengthened in order to lengthen the bone,which heals itself through a knitting process. This bone breakingprocedure is an excessively invasive procedure, requiring drilling theholes in the bone and inserting the chisel blade to actually create thefracture.

[0007] Moreover, fractures made by this procedure tend to be irregularand fragmented, making the bone more difficult to realign once the bonelengthening device is inserted into the bone marrow cavity.

[0008] Thus, there is a need for a bone breaking apparatus that willprovide an internally-created cut or stress concentration so that theresulting bone break is regular and easy to realign once a bonelengthening device is inserted into the cavity.

[0009] In an alternative procedure, a bone saw is placed within the bonemarrow cavity and the bone cut radially from within. However, thecutting depth cannot be controlled so that the depth of the cut can varyaccording to the thickness of the bone. Therefore, a single cut ofuniform depth is made, where the depth of the cut is limited by thethinnest portion of the bone in order to prevent damaging the periosteumand surrounding soft tissue at the thinnest point by cutting deeper.While the thinnest portion of the bone may be cut completely through,there are other areas which are only partially cut. Additionally, thistype of saw is incapable of cutting the bone along its length.

[0010] Further, such bone saws cannot be used for cutting the femur headdue to their large size and limited angular motion. In particular,features such as air inlet and exhaust hoses limit the angle to whichthe cutter head can be moved.

SUMMARY OF THE INVENTION

[0011] To overcome the disadvantages of the prior art, and in accordancewith the purposes of the invention, as embodied and broadly described inthe application, the invention provides a method of cutting a bone usinga bone cutting apparatus. The method includes determining a firstcutting depth based on variations in radial bone thickness of the bone,inserting a bone cutting apparatus having a cutting blade into a hollowspace within the bone, moving the cutting blade radially to set it tothe first cutting depth, cutting the bone at the first cutting depth,determining a second cutting depth based on variations in the radialbone thickness, adjusting the cutting blade radially to set it to thesecond cutting depth, and cutting the bone at the second cutting depth.

[0012] According to another aspect of the present invention, a bonecutting apparatus is provided. The bone cutting apparatus includes apower source, an articulating cutting assembly connected to the powersource and having a cutting blade, the cutting blade moveable between astored position and a cutting position, a cutting guide for guiding thecutting blade during bone cutting; and means for locking the bonecutting apparatus to a bone being cut, wherein at least a portion of thebone cutting apparatus including the cutting assembly is shaped to fitwithin a cylindrical cavity of a bone.

[0013] According to another aspect of the present invention, a poweredbone breaking mechanism is provided, comprising a machine spring, apowered spring having a compacted state and an expanded state, thepowered spring comprising a shape memory alloy, and a power sourceconnected to the powered spring.

[0014] According to one aspect of the present invention, a method ofbreaking a weakened bone is provided. The method includes attaching apowered bone breaking apparatus to a weakened bone, and moving a poweredspring of the apparatus from a compacted state to an expanded state.

[0015] According to a further aspect of the present invention, aminiature cutting device is provided. The miniature cutting devicecomprises a turbine and burr, a spherical turbine support housing,including two hemispherical turbine support housing portions, whereinthe turbine support housing portions fit together to form the sphericalturbine support housing and to hold the turbine and burr, and wherein afirst hemispherical turbine support housing portion includes slots fordirecting air onto blades of the turbine to rotate the turbine, twoouter cutter assembly support housing portions, wherein eachhemispherical turbine support housing portion is fitted to a respectiveouter cutter assembly support housing portion, wherein the outer cutterassembly support housing portion fitted to the first hemisphericalturbine support housing includes an air inlet passage for supplyingpressurized air to the slots of the first hemispherical turbine supporthousing, and means for rotating the turbine and burr about alongitudinal axis of the device.

[0016] According to yet another aspect of the present invention, amethod of removing an interior portion of a femur head is provided. Themethod comprises creating a small incision into skin below a hip of apatient to expose the femur, drilling a small hole into the femur,inserting a miniaturized femur cutter into the hole in the femur,rotating a turbine and burr of the miniaturized femur cutter at a highspeed to cut away a rotting, decayed, or cancerous section of the femurhead, changing the cutting angle as necessary by rotating the turbineand burr about a longitudinal axis of the miniaturized femur cutter, andremoving the miniaturized femur cutter from the femur.

[0017] Additional features and advantages of the invention will be setforth in the description that follows, and in part will be apparent fromthe description, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the system particularly pointed out in the writtendescription and claims hereof, as well as the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are incorporated in andconstitute a part of this specification, illustrate embodiments of theinvention and, together with the description, serve to explain theobjects, advantages, and principles of the invention.

[0019] In the drawings:

[0020]FIG. 1 is an isometric view of the bone cutting device of thepresent invention;

[0021]FIGS. 2A and 2B are a cross-sectional views of a first embodimentof the bone cutting device of the present invention;

[0022]FIG. 3 is a cross-sectional view of a first embodiment of acutting assembly of the present invention;

[0023]FIG. 4 is an isometric view of the body of the bone cutting deviceof the first embodiment of the present invention;

[0024]FIG. 5 is an exploded isometric view of a second embodiment of acutting assembly of the present invention;

[0025] FIGS. 6A-6C are side, front, and top views, respectively, of anembodiment of a guide mechanism of the present invention FIGS. 7A-7C areside views of alternative embodiments of a cutter guide of the presentinvention;

[0026]FIG. 8 is an isometric view of the second embodiment of thecutting assembly of the present invention shown in FIG. 5;

[0027]FIGS. 9A and 9B are isometric and top views, respectively, of aminiaturized femur head cutter of the present invention;

[0028]FIG. 10 is a dental drill using the turbine assembly of the cutterof FIGS. 9A-9D;

[0029]FIG. 11 is an exploded view of a cutter support housing of theminiaturized femur head cutter;

[0030]FIG. 12 is an exploded view of the miniaturized femur head cutter;

[0031] FIGS. 13A-13D are various views of a hemispherical turbinehousing of the miniaturized femur head cutter;

[0032] FIGS. 14A-14D are various views of the miniaturized femur headcutter with one cutter support housing and one hemispherical turbinesupport housing removed;

[0033]FIGS. 15A and 15B are enlarged views of FIGS. 14A and 14B,respectively;

[0034]FIG. 16 is an isometric view of an outer cutter support housing ofthe present invention;

[0035]FIGS. 17A and 17B are isometric and top views, respectively, of ahemispherical turbine support housing according to the presentinvention;

[0036]FIG. 18 is an exploded view of a second embodiment of the femurhead cutter of the present invention;

[0037] FIGS. 19A-19D are various views of the turbine support housing ofthe femur head cutter of FIG. 18;

[0038] FIGS. 20A-20D are various views of the rotation belt of the femurhead cutter of FIG. 18;

[0039]FIG. 21 is a side view of a bone breaking device of the presentinvention in a compacted state; and

[0040]FIG. 22 is a side view of the bone breaking device of FIG. 21 inan expanded state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] Reference will now be made in detail to the present preferredembodiments of the present invention, examples of which are illustratedin the accompanying drawings.

[0042] The bone cutting apparatus of this invention is designed toprovide a cutting blade that is capable of radial movement,circumferential movement, and movement along the longitudinal axis ofthe bone being cut. The cutting blade is intended to be capable ofvarying the depth of a cut around the circumference of the bone asnecessary in order to cut through the bone preferably in the form of a“Z” shaped cut, such that the blade has passes through the thickness ofthe bone at selected locations and breaches the outer circumference ofthe bone. That is, the “Z” cut bone cutting device is designed toprovide a guided means for cutting a section of bone from inside acavity created by removal of bone marrow within the bone through theouter circumference of the bone, allowing the bone to be easily brokenin preparation for a lengthening procedure.

[0043] According to one aspect of the invention, and as embodied in FIG.1, a bone cutting device 100 is provided and includes an upper bodyportion, a lower body support portion, and a cutting assembly. As shownin FIG. 1, upper body portion 101 may include actuating means foractuating the cutting assembly and handle means. Lower body portion 201may include guide means for guiding the cut made by the cuttingassembly, and means for supporting the device on the surgical site.Cutting assembly 301 may include a power source and a cutting tool.

[0044] According to one aspect of the invention, the bone cutting deviceincludes an upper body portion 101. As embodied herein and shown inFIGS. 1, 2A, 2B, and 4, upper body portion 101 of bone cutting device100 may include handle means 110. Handle means 110 may be formed ofmetal, or any other suitable material which is capable of beingsterilized so as to be surgically reusable. Alternatively, handle means110 may be made of a disposable material, such as a plastic, and beintended for a single use only. Handle means 110 is designed for thesurgeon to grasp and manipulate during the surgical procedure, therebyguiding and controlling the cutting of the bone.

[0045] Upper body portion 101 of bone cutting device 100 may alsoinclude actuating means 120 for actuating a cutting assembly 301 of thebone cutting device 100. As embodied herein and shown in FIG. 4, theactuating means 120 may include a thumb actuatable, pivoting projection130. Projection 130 is connected to the cutting assembly 301 such thatmovement of projection 130 causes a cutting tool of the presentinvention to move between a position close to being parallel to alongitudinal axis 140 of the bone cutting device, a storage position,and a position perpendicular to the longitudinal axis 140 of the bonecutting device, an in-use position. As shown in FIG. 4, projection 130may include a pulley lever attached to a pulley wheel. Projection 130may be made of any material suitable for sterilizing for medical use,such as stainless steel, titanium, or various polymers. Alternatively,projection 130 may be a button, a on/off switch, etc.

[0046] According to one aspect of the invention, the bone cutting device100 includes an lower body portion 201. As embodied herein and shown inFIGS. 4, 6, and 7, lower body portion 201 of bone cutting device 100 mayinclude a guide means for guiding the cutting of the bone. The guidemeans may include a cutting guide 220, as shown in FIGS. 4, 6, and 7,pictured as a tube or cylinder which circumferentially surrounds aportion of a central main shaft 225 of the bone cutting device 100.Cutting guide 220 has a slot or groove 230 which is in the shape of thecut to be made in the bone being cut. The guide means may also include apin 240 which acts as a groove follower pin, moving within and followingthe slot or groove 230 in cutting guide 220 to control the direction ofthe cutting and thereby the shape of the cut made.

[0047] In the presently preferred embodiment, groove 230 is shaped tocreate a “Z” cut which will be explained in more detail further on. Inorder to create the “Z” cut, groove 230 is formed in the shape of the“Z” to be cut into the bone. Thus, groove 230 has two semi-circulargroove portions 232, 234, which are diametrically opposed to oneanother, located on opposite sides of cutting guide 220 and aredistanced vertically from one another and connected to each other by twolongitudinal groove portions 236, 238. It may be desirable to create acut in a shape other than a “Z,” and for such a different cut, adifferent cutting guide 220 a, 220 b, 220 c with a differently shapedgroove 230 a, 230 b, 230 c may be provided as shown in FIGS. 7A, 7B, and7C. In each instance, cutting guide 220 a, 220 b, 220 c includes agroove 230 a, 230 b, 230 c formed into the shape of the desired cut inwhich a pin 240 will sit and follow to ensure that the bone is cut inthe desired shape. Examples of other types of desirable shapes for cutsinclude a radial cut which would use a circular groove, a longitudinalcut which would include a longitudinal groove, and a spiral cut whichwould use a spiral groove.

[0048] Cutting guide 220 is constructed to be removable from bonecutting device 101, and to be interchangeable with differently sized andshaped guides and with guides having differently shaped grooves forallowing differently shaped cuts, Cutting guide 220 must be of amaterial that is sterilizable, and sturdy enough to withstand anypressure applied by pin 240 in groove 230. Stainless steel and titaniumare examples of a suitable material.

[0049] Groove 230 may be a slot which extends completely through a widthof cutting guide 220, or it may be a deep or a shallow groove, dependentupon the type of pin used as follower pin 240. Alternatively, groove 230may consist of a raised portion or portions on cutting guide 220 whichpin 240 can follow.

[0050] The guiding means may also include a brace assembly 250. Braceassembly 250 is placed over main shaft 225 and cutting guide 220, and islocated between a cutting assembly support 299 and upper body portion101 of the cutting device 100. As embodied herein and shown in FIGS. 2A,2B, and 4, brace assembly 250 includes a brace arm 252 which is mountedabove cutting assembly support 299 about shaft 225. Brace arm 252supports the cutting device 100 and holds it in place against the boneduring the actual cutting procedure. A brace bottom 254 and a brace top256 fit over shaft 225 above brace arm 252, brace bottom 254 fittingtightly into a base portion of brace top 256 in order to hold it in adesired location. Brace top 256 includes follower pin 240 extendingthrough brace top 256 to sit within slot or groove 230 of cutting guide220.

[0051] As with other portions of the bone cutting device 100, braceassembly 250 should be sterilizable so as to allow it to be reusable insurgical procedures. In a preferred embodiment, brace assembly 250 ismade from stainless steel, but many other materials would be suitable aswould be obvious to one of ordinary skill in the art.

[0052] Brace assembly 250 is connected to main shaft 225 and moveablewith respect to shaft 225 with cutting guide 220. In use, the surgeonmanipulates brace assembly 250, causing pin 240 to follow the groove incutting guide 220, and thus controls the directional movement of thecutting tool as discussed in greater detail later.

[0053] According to one aspect of the invention, the bone cutting device100 includes a cutting assembly 301. As embodied in FIGS. 2A, 2B, 3, and5, cutting assembly 301 may include a power source for powering acutting tool. Although any suitably sized motor can be used, as well asother sources of power, the preferred embodiment utilizes an air turbine302, which minimizes the parts that are actually required to be kept ina cutting assembly 301 of the device. A cutting tool 304, hereinembodied as a burr, is rotated by the turbine 302 which is housed in thecutting assembly 301 in a turbine housing 306. Air is supplied toturbine 302 through flexible tubes 322 that extend from the cuttingassembly 301 to a source of air external from the bone cutting apparatus100. Additional flexible tubes 323 may be used to provide physiologicsolution (such as saline solution) to the cutting site to wash awaydebris and keep the cutting site and cutting tool cool. Turbine 302provides sufficient torque to cutter 304 such that cutter 304 penetratesthe hard material of the bone during use.

[0054] In a first embodiment shown in FIG. 3, air turbine 302 withintegral burr 304 is mounted in turbine housing 306 by a pair ofbearings 308. A housing end cap 310 is secured to turbine housing 306via clamp ring 312 and precisely locates air turbine 302 within turbinehousing 306. A pivot housing 314 includes a bore shaped to slidinglyreceive turbine housing 306, and turbine housing 306 is guided to movein a longitudinal direction along an axis 316 coincident with thecenterline of the burr 304, by a feed rack 318 which acts as a key forthe interface between turbine housing 306 and pivot housing 314. Asembodied in FIG. 3, there are two feed racks 318 diametrically opposedto one another and lying in a plane perpendicular to the axis of a pivotaxle 320. Flexible air lines 322 are attached to pivot housing 314, andpivot housing 314 includes suitable air passages to direct flow of airthrough corresponding passages in turbine housing 306 and into and outof the blades of air turbine 302.

[0055] According to another, more preferred embodiment of the presentinvention shown in FIGS. 5 and 8, in which similar numerals designatesimilar components, a bone cutting apparatus includes a turbine 402 anda burr 404 which are fixed in turbine housing 406 by a turbine lockingscrew 430. The turbine housing 406 preferably is mounted within acutting assembly support 499 by a pair of pivot pins 432. Thisconstruction allows turbine housing 406, and therefore turbine 402 andburr 404, to freely rotate between positions located at 0 degrees, whereburr 404 extends horizontally from the device and is perpendicular tothe main shaft 425 of the device, and a position approaching 90 degrees,where burr 404 is not extended but remains locked in an upright, nearvertical position adjacent to the main shaft 425 of the device (thestored position). By use of a locking mechanism to be discussed later,cutting assembly 401 can be fixed in any position from 0 degrees to thestowed position angle approaching 90 degrees. Thus, the depth of the cutmade in the bone, which is directly related to the angle of the burr,can be controlled and varied as the surgeon desires.

[0056] The cutting assembly 301, 401 is capable of rotating about thelongitudinal axis 226, 426 of the device, which coincides with thelongitudinal axis of the cavity in the bone so that the burr 304, 404can circumferentially cut into the inner surface of the bone. Burr 304,404 is also mounted in such a way that it can move radially toprogressively penetrate into the bone from the interior surface to theexterior surface thereof. This radial movement must be highly controlledin order to ensure that the cutter cuts only the bone and not thesurrounding flesh. Cutting assembly 301, 401 is mounted to a cuttingassembly support 299, 499 which provides bearing support forarticulation and controlled motion of cutting burr 304, 404.

[0057] The preferred type of cut will be referred to as a “Z” cut forits appearance in cross-section. The “Z” cut is generally formed in thefollowing manner. First, a surgeon inserts the cutting blade (burr 304,404) into the bone from the interior section thereof, and the cuttingassembly 301, 401 is rotated about the longitudinal axis 226, 426 of thedevice from the 0° position to the 180° position while the cutter 304,404 is cutting through the bone. This creates a semicircular cut in onetransverse plane of the bone. The cutting assembly 301, 401 is thencaused to move along the longitudinal axis of the bone a set distance.Once this set distance is reached, the cutting assembly 301, 401 isagain rotated about the longitudinal axis 226, 426 from the 180°position to the 360° or 0° position forming another semicircular cut inanother transverse plane of the bone, which is off-set from the firstplane by the distance moved along the longitudinal axis. The cuttingassembly 301, 401 is then longitudinally returned to its originalcutting position, thereby completing the Z cut in the bone. The cuttingprocess, using the first embodiment, follows a specific sequence asdiscussed below with respect to FIGS. 1, 2A, 2B, 3, and 4.

[0058] First, the cutting assembly 301 with cutter 304 in its stowedposition, shown in phantom in FIG. 2B, is inserted into the bone marrowcavity and cutting guide 220 is secured in place within the cavity.

[0059] The cutting blade (burr) 304 can be moved into its cuttingposition by the provision of a pivot drive blade 330, which is fixed atone end of the pivot housing 314 and can thus pivot the cutting assembly301 by being extended and withdrawn by a pivot adjustment nut 332located at the upper portion 101 of the bone cutting device 100. Sincethe pivot adjustment nut 332 is trapped in a slot 334 in a thrust collar336 located on the upper portion of the bone cutting apparatus, thereaction of the pivot adjustment nut 332 on the pivot drive threads 338on the pivot drive rod 340 causes the articulating cutting assembly 301to rotate until the rotation is forced to stop by contact of the sidesurface of a pivot bearing block 342. Air is caused to flow through theflexible air lines 322, thereby causing cutter 304 to turn at high speedin preparation for cutting. During rotation the cutter 304 iscontinuously turning and cuts a radial slot in the material of the bone.

[0060] The radial movement of the cutting assembly 301 may be providedby the provision of feed racks 318 that are contained in the cuttingassembly 301 and along the radial axis 323 of the cutter housing 306.Feed rack 318 may be actuated by a drive cable or pivot drive blade 330,located at the top of the cutting head support 299, which appliestension to a feed nut drive cable 344, which forces an adjustment nut332 to react against feed rack 318, thereby forcing the turbine housing306, turbine 302, and integral cutter burr 304 to move radially outwardto cut additional thickness of the bone.

[0061] If pre-surgical information about the bone cross-section at thiscut location dictates that cutter 304 should be projected radiallyoutward an additional amount, a partial rotation of a feed adjustmentnut 346 is made. This is done by rotating a cable drive adjuster 348located at the top of cutter head support 299 which applies tension tofeed nut drive cable 344. This rotation causes feed adjustment nut 346to react against feed rack 318 attached to turbine housing 306, therebyforcing the turbine housing 306, its integral bearing mounted airturbine 302, and its integral cutter 304 to move radially outward to cutadditional thickness of bone as the bone cross-section dictates.

[0062] The cutting action is continued by the operator as a suitabletorque is applied at the upper exposed end of cutter head support 299.Cutter 304, guided by groove follower pin 240 following groove portion232of groove 230 in cutting guide 220, cuts a prescribed radial swathfrom 0 degrees to 180 degrees. As embodied herein, grooves portion 236of groove 230 in cutting guide 220 allows the groove follower pin 240 tocut a longitudinal cut “x” inches in length in the bone in the “y”direction, after which another radial swath from 180 degrees to 360degrees is cut as pin 240 follows groove portion 234. Finally, a lastlongitudinal cut “x” inches in length is made in the bone in the “-y”direction, bringing cutter 304 back to its original starting position aspin 240 follows groove portion 238 of groove 230 in cutting guide 220.Once cutting is complete, cutter 304 is retracted to its stowed positionby a reverse rotation of pivot adjustment nut 332. The cutting method asoutlined above assumes a priori bone thickness information is usedperiodically during the cutting process to adjust the radial position ofcutter 304 to allow precision cutting through the bone thickness at eachlocation, thereby completing the “Z” cut and breaking the bone.

[0063] During this rotation, the cutter has been continuously turningand has cut a radial slot in the material of the bone. In thisembodiment of the invention, the slot that has just been cut is locatedat the 0° position of the cutting material so that the slot eventuallybecomes part of the Z cut in the bone.

[0064] Once the Z cut has been made in the bone, the bone cutting device100 is withdrawn from the cavity and the bone is either alreadycompletely broken in two or requires only a minor external force tocomplete the cut. Alternatively, the bone can be separated by a springactuated bone breaking mechanism as discussed below.

[0065] While this embodiment of the method of using the bone cuttingdevice accomplishes the desired “Z” cut, there are occasions where theshortening of a limb is desired. For this reason, a new cutting guide220 a would be incorporated where smaller sections of the bone would besevered around the periphery of the bone section to be removed. Onetechnique would be to start from the 0 degree position of the cutter 304where the articulated cutting head 301 is caused to rotate from itsstowed position to the position where the cutter 304 is perpendicular tothe longitudinal axis of the cutter head support 299, and from this 0degree position rotate the cutter 304 to +30 degrees then translatelongitudinally along the bone section “y” inches, the length of thesection to be removed, and to then rotate −30 degrees and then completethe severing of that section by translating longitudinally -“y” inches.This returns the cutter 304 to the 0 degree position. From 0 degrees, aswath of 60 degrees is cut through a translation cut of “y” inchesfollowed by a -30 degrees cut to sever another section of bone. Thereare infinite variations to this procedure where, for example, thesections are cut leaving a sliver of supporting bone until the entiresection has been cut. Thus, the final sliver can be fractured and/or cutand removed through the open bone marrow cavity.

[0066] The present invention also includes a spring actuated bonebreaking mechanism. The final breaking of the bone can be accomplishedby use of a spring actuated bone breaking mechanism 800, which reducesthe likelihood of uneven or fragmented breaking of the bone. The springactuated mechanism 800 of the present invention has two states, acompact state (FIG. 21) and an expanded state (FIG. 22).

[0067] As embodied herein and shown in FIG. 21, the powered bonebreaking mechanism 800 includes a machine spring 820 of a lengthsufficient to extend along substantial portions of both the upper andlower sections of the bone to be broken. Preferably, the spring is madefrom Nitinol or an equivalent phase change material. Also located insideof powered bone breaking mechanism 800 are several springs 830 comprisedof a shape memory material.

[0068] A shape memory material is a material which “remembers” itsoriginal shape when energy is supplied to the material, for example, byheating. The preferred shape memory material used in this invention isNitinol. As shown in FIG. 21, the shape memory springs 830 may includeBelleville washers 832. The washers 832 are flattened out into aweakened state, and stacked atop one another to form the springs 830.The springs 830 must have sufficient strength in order to stretch thesurrounding machine spring 820 which is locked to the bone at both thelower and upper portions, i.e., on either side of the weakened portionof the bone, and to overcome the breaking force of the section of thebone which has been weakened by the previously formed cut. Springs 830are preferably connected to a source of energy which heats the springsto change from a first phase to a second phase, the second phase being ashape which extends the length of the springs. As embodied herein andshown in FIGS. 21 and 22, the spring actuated mechanism 800 can betriggered to change state via a heater circuit 810 connected to themechanism 800. As shown, a heater resting outside the body may beattached to the spring portion via wires 812. Heat energy can besupplied to the spring formed by washers 832 by wire connection 812.When the heat is supplied, the Belleville washers assume their originalexpanded configuration. Alternatively, a battery may be permanentlyattached and encapsulated in the bone lengthening device to providepower to move the device between its compact state and its expandedstate.

[0069] The upper portion of the mechanism is rigidly attached to thebone by, for example, pins extending radially through the bone and intothe machine spring, and it is similarly locked in place in the lowersection of the bone. When triggered, the heater circuit 810 causes twoindependently attached longitudinal sections of the bone breaking deviceto separate from one another with force sufficient to separate thelongitudinal bone at the cut or weakened portion.

[0070] In yet another embodiment of the invention, a miniaturized femurhead cutter may be provided. Femur head cutter 500 eliminates the airsupply to turbine 302 through flexible tubes 322 of the cutting assemblyof FIGS. 1-8. This allows miniaturization of the cutting head to providea cutting tool for removal of the femur head and small enough to fitthrough a 10 mm hole, allowing a minimization of the invasiveness of thesurgical procedure. Additionally, such a miniaturized cutting head willallow freedom to move the cutting tool through a much larger angularexcursion, such as cutting a substantial portion of a full sphericalsurface. A larger angular excursion is desirable for machining away afemur head from inside the head. A generally hemispherical range ofmotion is necessary for such an action.

[0071] As shown in FIG. 10, such a miniaturized cutting tool is alsouseful to provide a dentist with a dental cutting head 600 to allow agreater range of movement for cutting and drilling at angles withrespect to a support handle of the drill.

[0072] As embodied herein and shown in FIGS. 9 and 11-17D, femur cutter500 includes a turbine 512, cutting tool 14, and support bearings 515assembled into a hemispherical turbine support housing. Thehemispherical turbine support housing includes a left half portion 532and a right half portion 516, each of which seals against a respectiveo-ring 536, 534 in a respective groove 540, 542 of a respective half ofan outer cutter support housing 534, 518 and pivots on an integral axle520. Right hemispherical turbine support housing portion 516 includes aseries of air directing slots 535 machined into turbine support housingportion 516 such that incoming air is directed along a path tangentialto blades 524 of the turbine 512 to cause rotation of the turbine. Lefthemispherical turbine support portion 532 also includes air directingslots 533 positioned to move the air along a path tangential to theturbine rotor 512. Slots 533 are cut at an angle to receive air from theturbine blades 524 and to direct it to an exhaust gas chamber 544 andthen to an air outlet passage 546. The right half of the outer cuttersupport housing 518 includes an air inlet passage 528 which directsincoming high-pressure air into a chamber 530 within the outer cuttersupport housing 518.

[0073] The hemispherical turbine support housing portions 516, 532 eachinclude an integral gear segment 548 a, 548 b about its periphery. Whenhemispherical turbine support housing portions 516, 532 are assembledwith turbine 512 and bearings 515, the adjacent gear teeth of the twosegments align with one another to form a single gear segment 548. Gearsegment 548 engages a pinion gear 550, which is installed in a cavity552 formed between outer cutter support housings 534, 518. Pinion gear550 includes pivot axles 554 which fit into and pivot on bearing bores556, 558 within the outer cutter support housings 534, 518.

[0074] An indexing shaft 560 nests between semicircular bearing seats562 in outer cutter support housings 534, 518. The indexing shaft 560includes a threaded portion 564 whose thread pitch 566 is compatiblewith the gear teeth spacing 558 of pinion gear 550.

[0075] As shown in FIG. 12, the femur cutter 500 can be installed in acutter guide assembly. The guide 570 is installed into a bore cut in thefemur and locked in place. The guide 570 provides a rotational bearingsurface for the longitudinal axis of the cutter support housing as wellas a means for controlling the rotation angle about the longitudinalaxis. The articulated cutting head is indexed by rotation of thethreaded indexing shaft 560 which is engaged to the pinion gear 550 andultimately engaged to the two hemispherical turbine support housingportions 532, 516. The indexing motion of the cutting head iscoordinated with the longitudinal positioning of a cam follower plate572. This is accomplished by threading the cam follower plate 572 andthe corresponding section of the indexing shaft 560. Thus, when theindexing shaft 560 is turned to change the angle of the cutting head,the cam follower plate 572 moves along the indexing shaft threads 561.This causes the cam follower surface 574 on the plate 572 to contact anew section of the cam surface, thereby allowing the cutting tool 514 totraverse rotationally about the longitudinal axis of the cutting headsupport and to remove a greater or lesser amount of the bone surface.

[0076] Guide pins 580 bridge the distance from the cutter supporthousing flange surface to the maximum travel of the cam follower plate572. Thus, when the cam follower plate handle is moved and a camfollower appendage 576 works within the restrictions of the cam surface,the cutting head also sweeps out the cam surface pattern as it cuts awaythe desired section of bone.

[0077] A retaining plate 578 is attached to the cutter guide housing tolock the cutter support housing into the guide housing, thus allowingonly rotation of the cutter support housing and its associated cuttinghead and cutting tool.

[0078] An alternative embodiment of the miniaturized femur head cutter700 is shown in FIGS. 18-20D. Instead of creating rotation of thecutting head with respect to the longitudinal axis of the cutting deviceby using gears and cam followers, a simpler mechanical structure isused. As embodied herein, the cutting assembly includes a turbine 712having a cutting tool 714. Turbine 712 is supported in a sphericalturbine housing 716, which is in turn supported within two halves ofanother cutter support housing 730, 732. Turbine housing 716 includesslots 733 to direct air received from air inlet 728 onto the blades ofturbine 712 as discussed above. Turbine housing 716 is also connectedvia pins 740 to a belt 742. Belt 742 also includes a first set ofconnecting holes 746 a. Connecting holes 746 a align with connectingholes 746 b in turbine housing 716 and belt 742 is held to turbinehousing 716 by pins 740. Belt 742 also includes a second set ofconnecting holes 748, to engage a gear 750 connected to an actuationlever 752. As actuation lever 752 is moved, teeth 751 of gear 750,engaged in the second set of connecting holes 748 of belt 742, causebelt 742 to rotate within slots 760 of outer cutter support housings730, 732. Belt 742 includes an open portion 745 to fit over cutting tool714 and for engaging turbine 712. As belt 742 rotates, it causes turbinehousing 716, and therefore turbine 712 and cutting tool 714 to rotatewith it.

[0079] The present invention also includes a preferred method ofoperating a miniaturized femur cutter to remove an interior portion of afemur head. According to this method, a small incision is made into theskin below the hip of the patient, exposing the femur. A hole is drilledinto the femur, and the device of the present invention is reinsertthrough the hole. Pressurized air is introduced into air inlet port 528of outer cutter support housing 518. The air enters chamber 530, andthen flows through slots 535 of hemispherical turbine support housing516 to blades 524 of the turbine 512, causing the turbine 512 to spin athigh speed. Ultimately this air exhausts out into the hemisphericalsupport housing chamber 538 and out of air outlet passage 546 of outercutter support housing 534 into the atmosphere.

[0080] The high speed rotation of the burr of turbine 512, allowscutting of the inside of the bone. In this instance, rotting, decayed,or cancerous sections of the femur head are cut and removed. During thecutting process, the turbine support can be pivoted on axles 520 tochange the cutting angle. Such pivoting is accomplished by rotating theindexing shaft 560 with respect to a longitudinal handle of the cuttingdevice. As indexing shaft 560 rotates, it engages and causes pinion gear550 to rotate, which in turn causes gear segment 548 to rotate,ultimately resulting in pivoting of turbine support 516, 532 about axles520. Using controlled movement of the device, the cutting tool is usedto sweep or cut out a section of the sphere forming the femur head.

[0081] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the disclosed process andproduct without departing from the scope or spirit of the invention.Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A bone cutting apparatus, comprising: a powersource; an articulating cutting assembly connected to said power sourceand including a cutting blade, said cutting blade moveable between astored position and a cutting position; a cutting guide for guiding saidcutting blade during bone cutting; and means for locking said bonecutting apparatus to a bone being cut, wherein at least a portion ofsaid bone cutting apparatus including said cutting assembly is shaped tofit within a cylindrical cavity of a bone.
 2. The bone cutting apparatusof claim 1 , further including means for continuously washing the boneas it is being cut.
 3. The bone cutting apparatus of claim 1 , whereinthe power source is an air turbine.
 4. The bone cutting apparatus ofclaim 1 , wherein the cutting blade is capable of cutting in a radialdirection around a circumference of the bone.
 5. The bone cuttingapparatus of claim 1 , wherein the cutting blade is capable of cuttingin a longitudinal direction along the long axis of the bone.
 6. The bonecutting apparatus of claim 1 , wherein the cutting blade is capable ofcutting in a radial direction around a circumference of the bone and ina longitudinal direction along the long axis of the bone.
 7. The bonecutting apparatus of claim 2 , wherein the means for continuouslywashing includes a pump and tubing for providing a physiologic salinesolution to a surgical site.
 8. The bone cutting apparatus of claim 1 ,wherein the cutting guide includes a cylinder having a groove in theshape of the cut to be made in the bone.
 9. The bone cutting apparatusof claim 1 , wherein the cutting guide includes a cylinder having agroove in the shape of the cut to be made in the bone, and wherein thegroove is shaped as a “Z.”
 10. The bone cutting apparatus of claim 9 ,wherein the cutting guide includes two semi-circular groove portions andtwo longitudinal groove portions.
 11. The bone cutting apparatus ofclaim 10 , wherein the two semi-circular groove portions arelongitudinally spaced away from and connected to each other by the twolongitudinal groove portions to form a continuous groove.
 12. The bonecutting apparatus of claim 11 , wherein the two semi-circular portionsare diametrically opposed from one another.
 13. The bone cuttingapparatus of claim 1 , wherein the cutting guide includes a cylinderhaving a groove therein, and a pin for following the groove to guide thecutting blade.
 14. The bone cutting apparatus of claim 1 , wherein thecutting assembly and the cutting blade are moveable to vary the depth ofa cut in the bone.
 15. The bone apparatus of claim 1 , wherein aposition of the cutting blade is radially adjustable to allow variationin the depth of a cut in the bone in a radial direction.
 16. The boneapparatus of claim 1 , wherein the cutting assembly is articulatable tomake a cut in a bone in a longitudinal direction.
 17. The bone apparatusof claim 1 , wherein the cutting assembly is articulatable to make a cutaround the circumference of the bone.
 18. The bone apparatus of claim 1, wherein the cutting assembly is articulatable to allow variation indepth of a cut in the bone in a radial direction, and to allow cuttingof the bone in both a longitudinal direction and around a circumferenceof the bone.
 19. A method of cutting a bone using a bone cuttingapparatus, comprising: determining a first cutting depth based onvariations in radial bone thickness of the bone; inserting a bonecutting apparatus having a cutting blade into a hollow space within thebone; moving the cutting blade radially to set it to the first cuttingdepth; cutting the bone at the first cutting depth; determining a secondcutting depth based on variations in the radial bone thickness;adjusting the cutting blade radially to set it to the second cuttingdepth; and cutting the bone at the second cutting depth.
 20. The methodof claim 19 , wherein determining a first cutting depth includesexamining at least one radiograph of the bone to be cut.
 21. The methodof claim 19 , wherein determining a second cutting depth includesexamining at least one radiograph of the bone to be cut.
 22. The methodof claim 19 , wherein the first and second cutting depths are the same.23. The method of claim 19 , wherein the first and second cutting depthsare different.
 24. The method of claim 19 , further including guidingthe cutting blade as it cuts the bone at the first depth.
 25. The methodof claim 19 , further including guiding the cutting blade during eachcutting step.
 26. The method of claim 25 , wherein the guiding stepincludes providing a cutting guide having a groove in the shape of thecut to be made.
 27. The method of claim 26 , further including followingthe shape of the groove with the cutting blade.
 28. The method of claim19 , further including using a cutting guide to guide the cutting bladeto create a cut in the bone in a desired shape.
 29. The method of claim28 , wherein the cutting guide guides the cutting blade to cut a “Z”shape into the bone.
 30. The method of claim 28 , further includingguiding the cutting blade to create a circumferential cut in the bone.31. The method of claim 28 , further including guiding the cutting bladeto create a longitudinal cut in the bone.
 32. A powered bone breakingapparatus comprising: a machine spring; a powered spring having acompacted state and an expanded state, the powered spring comprising ashape memory alloy; and a power source connected to the powered spring.33. The powered bone breaking apparatus of claim 32 , wherein the powersource is a heater circuit.
 34. The powered bone breaking apparatus ofclaim 32 , wherein the power source is a battery.
 35. The powered bonebreaking apparatus of claim 32 , wherein the powered spring comprisesNitinol.
 36. The powered bone breaking apparatus of claim 32 , whereinthe powered spring comprises Belleville washers.
 37. The powered bonebreaking apparatus of claim 36 , wherein the washers are flattened whenthe powered spring is in its compacted state.
 38. The powered bonebreaking apparatus of claim 36 , wherein the washers are not flat whenthe powered spring is in its expanded state.
 39. A method of breaking aweakened bone, comprising: attaching a powered bone breaking apparatusto a weakened bone; and moving a powered spring of the apparatus from acompacted state to an expanded state.
 40. The method of claim 39 ,wherein the attaching step includes attaching a first end of a machinespring to the bone above the weakened portion and attaching a second endof the machine spring to the bone below the weakened portion.
 41. Themethod of claim 39 , wherein the moving step includes applying heat tothe powered spring to cause it to move from its compacted state to itsexpanded state.
 42. A miniature cutting device comprising: a turbine andburr; a spherical turbine support housing, including two hemisphericalturbine support housing portions, wherein the turbine support housingportions fit together to form the spherical turbine support housing andto hold the turbine and burr, and wherein a first hemispherical turbinesupport housing portion includes slots for directing air onto blades ofthe turbine to rotate the turbine; two outer cutter assembly supporthousing portions, wherein each hemispherical turbine support housingportion is fitted to a respective outer cutter assembly support housingportion, wherein the outer cutter assembly support housing portionfitted to the first hemispherical turbine support housing includes anair inlet passage for supplying pressurized air to the slots of thefirst hemispherical turbine support housing; and means for rotating theturbine and burr about a longitudinal axis of the device.
 43. Thecutting device of claim 42 , wherein the cutting device is a femur headcutting device.
 44. The cutting device of claim 42 , wherein the cuttingdevice is a dental drill.
 45. The cutting device of claim 42 , wherein asecond of the two hemispherical turbine support housings includes airdirecting slots for receiving air from the turbine blades and to directthe air toward an air outlet passage.
 46. The cutting device of claim 45, wherein the outer cutter assembly support housing portion fitted tothe second hemispherical turbine support housing includes the air outletpassage.
 47. The cutting device of claim 42 , wherein the means forrotating the turbine and burr about the longitudinal axis of the deviceincludes a gear formed on the turbine support housing.
 48. The cuttingdevice of claim 42 , wherein the means for rotating the turbine and burrabout the longitudinal axis of the device includes a belt attached tothe turbine support housing.
 49. The cutting device of claim 48 ,wherein the means for rotating the turbine and burr about thelongitudinal axis of the device further includes a gear and actuationlever, wherein a first end of the belt is connected to the sphericalturbine housing and wherein a second end of the belt is connected to thegear.
 50. A method of removing an interior portion of a femur head,comprising: creating a small incision into skin below a hip of a patientto expose the femur; drilling a small hole into the femur; inserting aminiaturized femur cutter into the hole in the femur; rotating a turbineand burr of the miniaturized femur cutter at a high speed to cut away arotting, decayed, or cancerous section of the femur head; changing thecutting angle as necessary by rotating the turbine and burr about alongitudinal axis of the miniaturized femur cutter; and removing theminiaturized femur cutter from the femur.